The present invention relates to a method and an apparatus for assessing the effect of yarn faults on woven or knitted fabrics produced from the respective yarn by simulation of the fabric image.
Traditional methods of this type use so-called display boards for simulating the fabric image. The respective yarn is wound spirally around trapezoidal or rectangular pieces of cardboard or metal sheets, thereby forming a kind of quasi woven or knitted fabric, from which possible fault patterns can be seen clearly. The display boards are therefore a valuable aid in estimating whether and to what extent a particular yarn is suitable for a particular fabric, and they allow predictions to be made on one of the most important quality features of the finished product, namely its appearance.
However, the production of the display boards by the winding of yarn around metal sheets is relatively labor intensive and is also no longer in keeping with the times, so that there is a need for a new method for simulating the fabric image. This new method should necessitate as little outlay as possible in terms of labor, it should be flexible and it should give reliable and reproducible results.
According to the invention, the following steps are carried out to assess the effects of yarn faults on the appearance of fabrics containing such yarns:
a. examination of the yarn for parameters associated with the volume and/or the diameter and/or the surface;
b. conversion of said parameters into grey values or color values and assignment of these values to image spots; and
c. reproduction of the image spots to produce an image which represents a simulation of a woven or knitted fabric produced from the examined yarn.
An apparatus according to the invention is characterized by a measuring member for determining parameters associated with the volume and/or the surface of the yarn, by a computer for converting said parameters into grey or color values, by means for assigning the grey or color values to image spots, by a video display unit and/or a printer, and by control means for reproducing the image spots on the video display unit and/or on the printer for the purpose of simulating a woven or knitted fabric produced on the examined yarn.
By means of the invention, therefore, the display boards are produced electronically, and if a uniformity tester, such as, for example, the testers sold by Zellweger Uster AG under the designation USTER TESTER (USTER being a registered trademark of Zellweger Uster AG), is used as a measuring device for examining said parameters, the electronic display boards are calculated from the data conventionally produced. With the USTER TESTER, which is described by way of example in EP-A-0 249 741 and in CH-A-671 105 (the disclosures of both of which are incorporated herein by reference), the uniformity and/or the hairiness of a yarn sample among other things are examined and are represented in the form of a graph, a wavelength spectrum or other graphical representations of the variations of the measured parameters on a video display unit and/or on a printer. Uniformity and hairiness are two parameters which are essential for the later fabric image and which can be processed at a relatively low outlay in terms of software in order to simulate the display boards.